@polotek
I'm usually very picky about it and want my computer to be idle when it's idle, like below 1% load. And usually I had to resort to various tricks to achieve it like unloading all tabs manually and even sending STOP signal to Firefox to freeze it when I'm not using it.
But now… I no longer have to. I mean yeah, it still wakes up occasionally and consumes a couple of percents of CPU when in the background, but it's barely noticeably even on my aged hardware.
They did an outstanding job!